1. Field of the Invention
The present invention relates to a method for manufacturing a base for an electrode plate that can be used in a storage battery, a method for manufacturing a positive electrode plate, and an alkaline storage battery.
2. Description of Related Art
Nickel positive electrodes for alkaline storage batteries are classified mainly into a sintered type and a non-sintered type. Suggested as an example of the latter non-sintered type positive electrodes are the ones obtained by supporting nickel hydroxide particles with a nickel foam substrate having a porosity of about 95% (see JP 56(1981)-37665 B, JP 56(1981)-20664 B and JP 57(1982)-30268 B), which are in wide use currently. However, the nickel foam substrate is expensive because its manufacturing method is complicated.
On the other hand, substrates such as a punched sheet and an expanded metal are inexpensive because they can be formed by processing metal foils. However, these substrates do not have a three-dimensional structure, causing a problem in that an active material sheds from the substrate easily.
In order to solve such a problem, an attempt has been made to manufacture a substrate by processing a metal foil three-dimensionally. For example, it is reported that a metal foil is processed so as to provide a substrate with both sides on which protrusions are formed (see JP 6(1994)-79065 U). However, even when using this substrate, the active material cannot be prevented from shedding sufficiently.
On the other hand, a method for manufacturing the sintered type nickel positive electrodes includes forming a base having nickel layers with a porosity of about 85% on the surfaces of a metal support, immersing this base in an aqueous solution containing nickel nitrate as a main solute, then immersing it in an alkaline solution containing sodium hydroxide as a main solute, thereby filling nickel hydroxide in the base. Thereafter, the above processes are repeated until the nickel hydroxide is filled in a predetermined amount. However, with this method, it has been difficult to achieve a higher capacity because the support has a porosity of only 85%. In response to his, JP 2951008 B discloses a method including producing a base having a porosity of 90% or more and filling it with nickel hydroxide by the above-described method. Ithis case, the base having a porosity of 90% or more is produced by using paste to which hollow particles are added.
However, this method has the following problems: (1) When immersing the base in nickel nitrate, the corrosion of metal lowers a cohesive strength between the metal support and the porous nickel layers, thus separating them in some cases. (2) When substituting alkali for nickel nitrate, since an active material to be deposited has a large specific surface area, it has been difficult to fill the active material densely. (3) When filling the active material, it has been very difficult to disperse an electrically conductive agent such as a cobalt compound uniformly between the active materials and to use as the active material nickel hydroxide with which an additive such as a zinc compound forms a solid solution. If no additive is allowed to form a solid solution with it as described above, there is a problem that a longer lifetime cannot be achieved.
In view of the problems described above, it is an object of the present invention to provide a method for manufacturing a base for an electrode plate that has an excellent ability to retain an active material and can be manufactured at a low cost, a method for manufacturing a positive electrode plate, and an alkaline storage battery using the same.
In order to achieve the above-mentioned object, a first method for manufacturing a base for an electrode plate according to the present invention is a method for manufacturing a base for an electrode plate used as an electrode plate of a storage battery and includes (i) forming a slurry containing water, a powder containing nickel, and a hollow particle formed of an organic compound, (ii) applying the slurry to a support made of metal, thereby forming a sheet, and (iii) burning the sheet, thereby forming a porous layer joined to the support by a metallic bond. This first manufacturing method makes it possible to manufacture the base for an electrode plate of the present invention easily.
In the above-described manufacturing method, the powder may be adsorbed on a surface of the hollow particle. In this case, the slurry may contain stearic acid, and the powder may be adsorbed on the hollow particle via the stearic acid. With this structure, the powder containing nickel can be adsorbed on the particle easily.
In the above-described manufacturing method, the slurry may contain a thickener. With this structure, the dispersiveness of the powder containing nickel improves, thus obtaining a base having a porosity with more uniform distribution. In this case, the thickener may contain at least one selected from the group consisting of cellulose, a cellulose derivative and polyvinyl alcohol. With this structure, it is possible to obtain a base having less variation in thickness and a porosity with more uniform distribution.
In the above-described manufacturing method, the hollow particle may contain a polymer formed by polymerizing a monomer containing at least one selected from the group consisting of methyl methacrylate, acrylonitrile and vinylidene chloride, and at least one selected from the group consisting of isobutane, isopentane and isooctane may be sealed in the hollow particle. With this structure, the particle can be expanded easily by a heat treatment.
In the above-described manufacturing method, the hollow particle in the (i) forming may have a diameter ranging from 10 to 40 xcexcm, and after the (ii) applying and before the (iii) burning, the method may include the process of expanding the hollow particle by heat-treating the sheet so that the hollow particle achieves a maximum diameter ranging from 100 to 300 xcexcm. With this structure, the dispersiveness of the particle in the paste during the (i) forming improves, thus obtaining a base having a porosity with more uniform distribution.
In the above-described manufacturing method, the hollow particle in the (i) forming may have a diameter ranging from 100 to 300 xcexcm. With this structure, a stronger base can be obtained.
In the above-described manufacturing method, the powder may contain at least one material selected from the group consisting of a metallic nickel and a nickel compound. With this structure, a porous layer made of nickel can be formed easily.
Furthermore, a first method for manufacturing a positive electrode plate for an alkaline storage battery according to the present invention includes filling a base with a slurry containing a binder and an active material powder containing nickel hydroxide, followed by drying and rolling. The base includes a support made of metal and a porous layer formed on the support. The porous layer is made of nickel and has a porosity ranging from 90% to 98%. The support and the porous layer are joined by a metallic bond.
Moreover, a second method for manufacturing a positive electrode plate for an alkaline storage battery according to the present invention includes (I) filling a base with an active material powder containing nickel hydroxide and rolling it, thereby forming a sheet including the base and an active material filled in the base, (II) immersing the sheet in a solution in which a binder is dispersed, thereby making the binder adhere to a surface of the sheet, and (III) drying and rolling the sheet to which the binder has adhered. The base includes a support made of metal and a porous layer formed on the support. The porous layer is made of nickel and has a porosity ranging from 90% to 98%. The support and the porous layer are joined by a metallic bond. The above-described first and second manufacturing methods employ a base having an excellent ability to retain an active material, and therefore, with these manufacturing methods, a positive electrode plate that makes it possible to constitute an alkaline storage battery with excellent high-rate discharge characteristics, a high capacity and a longer lifetime can be provided. In addition, since a base that can be provided at a low cost is used, a positive electrode plate can be manufactured at a low cost.
In the above-described first and second methods for manufacturing a positive electrode plate, the support may be a processed foil obtained by forming protrusions on a surface of a metal foil or a punched metal sheet obtained by forming through holes in a metal foil, and the metal foil may be a nickel foil formed by electroplating or a metal foil whose surface is coated with nickel. With this structure, a positive electrode plate that makes it possible to constitute an alkaline storage battery with a high power and a high capacity can be provided at a low cost.
In addition, an alkaline storage battery according to the present invention includes a positive electrode plate. The positive electrode plate includes the base for an electrode plate manufactured by the manufacturing method of the present invention, and an active material powder containing nickel hydroxide filled in the base. Since an alkaline storage battery of the present invention employs the base manufactured by the manufacturing method of the present invention, it is possible to achieve a storage battery having excellent charge-discharge cycle characteristics, a storage battery having a large discharge capacity when discharged with a large electric current, or a storage battery having a high utilization factor of a positive electrode.